The present invention relates to a voltage boosting technique in a semiconductor memory and, more particularly, to a technique effective when applied to control of a boosted voltage in an EEPROM (Electrically Erasable and Programmable Read Only Memory).
In recent years, an IC card having the functions of a credit card and a telephone card is being spread. The IC card is a card having a shape similar to that of a magnetic card and on which a CPU and a memory are mounted. Reading/writing on the memory is controlled by the CPU. The card itself has a ciphering function and therefore has a high security function and large storage capacity.
There are IC cards of a contact type having, as one of means for transmitting/receiving information to/from an external device such as a reader/writer, mechanical coupling means to the external device, a non-contact type for transmitting information via an information transmitting medium such as waves, and a so-called dual way type of a contact/non-contact type.
An IC card of the non-contact type, in the vicinity of an external device, receives electric waves emitted from the external device. Current flows in a coil as an antenna provided in the IC card by electromagnetic induction, an alternating current voltage is applied to a semiconductor integrated circuit device to which both ends of the coil are connected, thereby supplying power.
The semiconductor integrated circuit device converts the supplied alternating current voltage to a direct current voltage by a rectifying circuit, generates an internal power source voltage Vdd via a regulator, and supplies it to modules.
In an IC card, an EEPROM is widely used as a memory. The EEPROM is an electrically erasable and programmable read only memory and stores data to be input/output to/from the IC card.
The EEPROM has a voltage boosting circuit constructed by a charge pump circuit and the like. The voltage boosting circuit generates a write voltage and an erase voltage used for data writing operation from the internal power source voltage supplied via the regulator.
Examples of the semiconductor memory of this type are a flash memory which performs a time division process to suppress peak current (refer to Japanese Unexamined Patent Publication No. 2002-109894) and an EEPROM in which voltage boosting speed is controlled to be constant irrespective of load capacity (refer to International Publication No. W02-19342).